You've probably heard of peanut or shellfish allergies. But a meat allergy? Not as common. Even weirder is what might be causing it—tick bites, according to a study in the Journal of General Internal Medicine. [Susan E. Wolver et al., A Peculiar Cause of Anaphylaxis: No More Steak?]

A few years back, folks started showing up in emergency rooms in the southeast U.S. with hives, swelling or worse—anaphylaxis—after eating red meat. For this study, researchers looked at three of those cases. And they found that tick bites, specifically those of the Lone Star tick, seem to be the cause.

The bitten victim’s immune system appears to become sensitized to a substance called alpha-gal. And whereas all the major food allergies are triggered by proteins, the culprit here—alpha-gal—is a carbohydrate.

Alpha-gal is found in the meat and fat of hooved mammals, like cows, sheep or pigs. So eating a burger can expose you to alpha-gal, which activates antibodies and leads to the release of histamines.

Researchers say something similar to alpha-gal in the tick saliva may set off the immune system—which then goes after the alpha-gal in meat. And leaves a steak lover ticked off.